The present invention relates generally to snowmobiles. More particularly, the present invention relates to methods and apparatus for propelling snowmobiles.
Since their development in the middle of the 20th century, snowmobiles have gained widespread popularity. Snowmobiles are commonly used for trail riding and utility applications. Perhaps the most common snowmobile application is recreational trail riding. Trail riding on a snowmobile allows a snowmobile enthusiast to travel through areas which are not accessible by other types of vehicles. For example, snowmobiles can travel very rapidly across frozen lakes during the winter in northern climates. Modern snowmobiles, can cover ground very rapidly and can cover great distances. Frequently, snowmobile enthusiasts ride their snowmobile for many hours straight and cover many miles.
A rider operates a snowmobile by providing inputs such as acceleration inputs provided using a throttle, deceleration inputs provided using a brake, and steering inputs provided using a set of handle bars. The rider may also influence the performance of the machine by shifting his or her weight, for example, by leaning into a turn.
Frequently, people become interested in snowmobiling because of the unique riding experience that snowmobiles provide. Part of the thrill of riding a snowmobile is encountering challenging terrain, and traversing that terrain through a combination of the skill of the rider and the way that the snowmobile reacts to the inputs provided by the rider. Aspects of a snowmobile such as the overall weight of the snowmobile, the weight distribution of the snowmobile, and the location of the snowmobile center of gravity all effect the riding experience enjoyed by a snowmobiling enthusiast.
The ability of a rider to traverse challenging terrain smoothly and quickly frequently depends upon the way that the snowmobile responds to the rider. As mentioned previously, the rider can control the snowmobile by providing inputs using the handlebars, brake and throttle. The rider can also control the snowmobile by selectively shifting his or her weight.
The way that a particular snowmobile responds to inputs provided by a rider may depend upon the snowmobile""s total inertia, the snowmobile""s moment of inertia, and the location of the snowmobile""s center of gravity. The total inertia of a snowmobile has an effect on that snowmobile""s performance because this total inertia determines the extent to which the snowmobile will resist changes in location and linear velocity. For example, the inertia of an overly heavy snowmobile may limit how rapidly that snowmobile can accelerate and decelerate. The moment of inertia of a snowmobile also has an effect on that snowmobile""s performance, since it determines the extent to which the snowmobile will resists changes in angular position and rotational velocity. The moment of inertia of a snowmobile is determine, at least in part by the total mass of the snowmobile the way in which that mass is distributed.
The present invention relates generally to snowmobiles. More particularly, the present invention relates to methods and apparatus for propelling snowmobiles. A snowmobile in accordance with an illustrative implementation of the present invention comprises a chassis defining a tunnel, a drive shaft at least partially disposed in the tunnel, and at least one drive sprocket fixed to the drive shaft. A drive track overlays a portion of the at least one drive sprocket, and an inner surface of the drive track defines an interior of the drive track.
In one aspect of the present invention, a bearing is disposed within the interior of the drive track for rotatably supporting the drive shaft. In some implementations of the present invention, the bearing is supported by a housing having a first portion fixed to the chassis and a second portion extending into the interior of the drive track. The housing may be selectively fixed to the chassis, for example, by a plurality of threaded fasteners.
The drive shaft is preferably operatively coupled to an engine by a drivetrain. In one advantageous implementation, the drivetrain comprises a reduction mechanism that is substantially disposed within the tunnel defined by the chassis. In a particularly advantageous implementation, the reduction mechanism is disposed within a projection extending from a drive sprocket fixed to the drive shaft.
In one illustrative implementation of the present invention, the speed reduction mechanism includes a first gear fixed to the drive shaft and a second gear engaging the first gear so that a plurality of teeth of the second gear are intermeshed with a plurality of teeth of the first gear. The first gear advantageously has a first pitch circle that is different from a second pitch circle of the second gear. The first pitch circle and the second pitch circle may be advantageously selected to provide a desired gear ratio. In certain implementations, the first gear comprises a ring gear and the second gear comprises a spur gear disposed within a cavity defined by the ring gear. In certain implementations, both the first gear and the second gear are disposed within a cavity defined a housing.
In one aspect of the present invention, the speed reduction mechanism is disposed below a reference plane defined by a top surface of the drive track. Placing the speed reduction mechanism in a relatively low position may serve to lower the center of gravity of a snowmobile including the speed reduction mechanism. A snowmobile with a lower center of gravity may be more stable and is less likely to overturn.
In an additional aspect of the present invention, a speed reduction mechanism having a compact shape is provided. In certain advantageous implementations, the compact shape of the speed reduction mechanism allows the speed reduction mechanism to be disposed within an interior defined by the inner surface of the drive track. In certain particularly advantageous implementations, the compact shape of the speed reduction mechanism allows the speed reduction mechanism to be disposed within a projection extending from a drive sprocket coupled to the speed reduction mechanism by a drive shaft. Providing a speed reduction mechanism having a compact arrangement, and positioning this speed reduction mechanism in a central location of a snowmobile may serve to provide a snowmobile having a reduced moment of inertia. When a snowmobile has a reduced moment of inertia the rider can more easily make quick changes in the angular orientation and rotational velocity of the snowmobile.
In yet another aspect of the present invention, a speed reduction mechanism may be provided which has less rotating mass than other types of speed reduction mechanisms. Providing a speed reduction mechanism with a lower rotating mass serves to provide a snowmobile having quicker acceleration. Quick acceleration may be advantageous in high performance applications such as snowmobile racing.
In still another aspect of the present invention, a method for easily changing the gear ratio of a speed reduction mechanism is provided. This method allows a rider to change the gear ratio to tune the snowmobile for a particular set of riding conditions. A method of changing a gear ratio of a drivetrain in accordance with the present invention may comprise the steps of 1) providing a speed reduction mechanism including a ring gear fixed to a drive shaft, 2) providing an original assembly fixed to the speed reduction mechanism, the original assembly including an original drive gear rotatably supported by an original mounting plate, 3) providing a new assembly including a new drive gear rotatably supported by a new mounting plate, the new drive gear having an effective diameter different than an effective diameter of the original drive gear, 4) removing the original assembly from the speed reduction mechanism, and 5) installing the new assembly onto the speed reduction mechanism.